Optical fibers are finding increasing use in telecommunications as well as in other date transmission systems because of their ability to carry vastly more information than equivalent sizes of electrical wire. Connecting two or more optical fibers, however, requires much more care than equivalent electrical connections since the fibers must be optically aligned. Many forms of optical connectors have been proposed to achieve the direct compatibility of such connections, and include butt-to-butt joints of cleaved and polished fibers, and expanded beam lenses.
This invention is particularly concerned with improving the latter. Such expanded beam lenses are shown in, i.e., U.S. Pat. Nos. 4,691,985; 4,671,609; 4,678,268; 4,687,285; 4,693,556; 4,456,330; 4,497,536; 4,380,365; 4,327,963; 4,370,021; 4,304,461; 4,290,667; 4,269,648; 4,265,699; 4,265,511; and 4,193,633.
The lenses shown can be broken down into three basic types, viz: add-on lenses that are slipped over the end of a fiber; spherical lenses that are cemented to a fiber end; and lenses formed by deformation of the fiber end itself.
While all of these techniques have been employed with greater of lesser degrees of success, all have some problems, such as difficulty of field use, high cost or lack of consistent performance. Plastic lenses have suffered because of their different thermal expansion coefficients when compared with glass.
This invention is particularly concerned with add-on lenses.